Secondary batteries which are highly applicable to various products and exhibit superior electrical properties such as high energy density, etc. are commonly used not only in portable devices but also in electric vehicles (EVs) or hybrid electric vehicles (HEVs) driven by electrical power sources. The secondary battery is drawing attentions as a new energy source for enhancing energy efficiency and environment friendliness in that the use of fossil fuels can be reduced greatly and no byproduct is generated during energy consumption.
Secondary batteries widely used at the preset include lithium ion batteries, lithium polymer batteries, nickel cadmium batteries, nickel hydrogen batteries, nickel zinc batteries and the like. An operating voltage of the unit secondary battery cell, namely a unit battery cell, is about 2.5V to 4.2V. Therefore, if a higher output voltage is required, a plurality of battery cells may be connected in series to configure a battery pack. In addition, depending on the charge/discharge capacity required for the battery pack, a plurality of battery cells may be connected in parallel to configure a battery pack. Thus, the number of battery cells included in the battery pack may be variously set according to the required output voltage or the demanded charge/discharge capacity.
Meanwhile, when a plurality of battery cells are connected in series or in parallel to configure a battery pack, it is common to configure a battery module composed of at least one battery cell first, and then configure a battery pack by using at least one battery module and adding other components.
A conventional battery module includes a plurality of stacked battery cells and a bus bar assembly for electrically connecting electrode leads of the plurality of battery cells.
Here, the bus bar assembly includes a bus bar frame having lead slots through which the electrode leads of the battery cells pass individually, and a bus bar mounted to the bus bar frame and having bus bar slots corresponding to the number of lead slots, so that the bus bar is connected to the electrode leads passing through the bus bar slots by welding or the like.
However, in the conventional battery module, since the lead slots are required as much as the number of the electrode cells, the number of lead slots is increased according to the number of the electrode leads. Also, as the number of lead slots is increased, intervals of the lead slots are relatively narrowed at the bus bar frame, which may deteriorate the efficiency of the assembling process, for example by increasing the probability of assembly failure such as misassembling according to the number of electrode leads.
Therefore, in the battery module, it is required to find a way to improve the efficiency of the assembly process when the bus bar assembly is assembled to the battery cell.